Critical interpretation of urinary phencyclidine monitoring.

A critical appraisal of issues and problems in monitoring urinary phencyclidine (PCP) is presented. Problems may be related to impurities of ingested material and/or metabolites, and methods that are not sensitive enough to detect PCP in the nanogram/ml amounts which may be present in blood or urine. Possible false positives found with some methods are discussed. Most complicated of all is the unpredictable excretion of PCP which can result in negative urines followed by urines which test positive for PCP without necessity of any further ingestion of PCP. A set of guidelines for use in monitoring and interpreting PCP values is included.